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Re: [Qemu-devel] [PATCH v2 1/1] KVM s390 pci infrastructure modelling

From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH v2 1/1] KVM s390 pci infrastructure modelling
Date: Sat, 4 Jul 2015 20:25:23 +0200

On Fri, Jul 03, 2015 at 07:09:59PM +0800, Hong Bo Li wrote:
> >But I would like to note that pci device drivers require driver handshake
> >before device goes away.
> >IIUC s390 hotplug is immediate, which is a problem.
> >Maybe doing the change will help make sure device removal is acked
> >by guest before it happens?
> >
> I did some prototype today. If define zpci first, the progress of unplug
> will get complicated.

The point is that you don't have to remove the zpci device at all.
Remove pci device from zpci.

I think the complication you refer to is the guest ack of
the removal, isn't it?
It's complicated, but it has a chance to actually work with
pci device drivers.

This, as opposed to just removing the device whenever host
tells us to.

> So I prefer defining vfio pci first.
> And it looks like the vfio pci is the basic device, if we want this
> vfio pci to work on s390, we have to define a zpci device to give some
> additional information to it.

if vfio connects to the bus internal to zpci, it can get
things from the bus in a natural way.

If zpci is connected to vfio, it becomes much messier.


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